1. Field of the Invention.
The field of the invention relates to needle assemblies for performing anesthesia procedures, particularly during childbirth.
2. Brief Description of the Prior Art.
Various instruments have been devised for providing local anesthetic during childbirth. During the first stage of labor, pain caused by dilation of the cervix may be relieved by a paracervical block. Pain at the time of delivery may be relieved with a transvaginal pudendal block.
In order to prevent accidental lacerations or punctures, pudendal/paracervical block anesthesia needle assemblies generally include a needle guide which is properly positioned within the patient prior to pushing the needle therethrough. It is also important to control the depth of needle penetration, and the needle guide should include means for limiting such penetration to less than a predetermined depth, such as about fifteen millimeters.
U.S. Pat. Nos. 2,700,385; 2,712,314; 2,880,724; 3,380,448; 3,995,629 and 4,275,728 disclose various instruments for performing pudendal/paracervical blocks or for administering other medicaments. The latter two patents disclose means for controlling the extent to which the needle tip will project from the needle guide. Specifically, the instruments disclosed in U.S. Pat. Nos. 3,995,629 and 4,275,728 allow the needle to be maintained in three positions: a retracted position, and two different extended positions to permit two different injection depths.
Another well known instrument for providing pudendal and/or paracervical blocks includes a needle guide comprising a handle, an elongate, open-ended tube secured to the handle, and an enlarged patient contacting tip member secured to the distal end of the tube. A needle having a hub on one end may be inserted through the tube until the hub contacts the proximal end of the tube. The needle is longer than the tube and, accordingly, the needle tip will protrude through the enlarged tip member. If the physician wishes to expose less of the needle tip, he or she must remove the needle from the tube and slip a separate movable needle collar over the needle and then re-insert the needle into the tube. This procedure is undesirable because it could result in needle point damage and/or accidental needle sticks. The needle collar engages the proximal end of the tube instead of the hub when the needle is inserted so that less of the needle protrudes through the enlarged tip member.